1. Field of the Invention
This invention relates to a heat exchanger which uses a drag reducing fluid as its heat transfer medium. Heat exchangers of this type are used in district heating/cooling systems, heat transportation systems for heating and cooling, and industrial processes that employ hot water as a heat transfer medium in the production of chemical products, processed foods and the like.
2. Description of the Prior Art
The drag that arises between the surface of the heat exchanger and the heat transfer medium with which it exchanges heat is known to increase the amount of pumping power required for circulating the heat transfer media. When a heat transfer medium such as hot water is pumped through a long pipeline in a district heating system, for example, the system is required to have very large pumping power to overcome the drag between the heat transfer medium and the pipe wall. Since a reduction in drag translates into a reduction in the required pumping power, it has been proposed to use a drag reducing fluid (DR fluid) as the heat transfer medium. It is known that a DR fluid, which is water mixed with a surfactant or a water-soluble polymer, can reduce drag in a pipeline to about one fifth that of water alone. From this it follows that the pumping power cost which accounts for 30% of the operating expense of a district heating system could be reduced to about one fifth by use of a DR fluid as the heat transfer medium. (Bewesdorff, H. W., Structure of Turbulence and Drag Reduction, (1990), 293, Springer et al.)
It is widely known, however, that the drag reduction obtained by use of a DR fluid comes at the expense of a loss in the heat exchange performance of the heat exchanger. Application of DR fluid-based drag reduction technology to a district heating system therefore requires installation of a large and complicatedly configured heat exchanger. As a result, the initial investment is large and the reduction in pumping power is not as great as might be hoped.
This invention was accomplished in light of the foregoing circumstances and has as its object to provide a heat exchanger which utilizes the special properties of a DR fluid to achieve small drag while also achieving high heat exchange performance in the heat exchanger.